For a more detailed introduction to this guide please read the port bis guide for the 10-19 bracket. I go into more depth there into stuff like what race you should choose and how to navigate these guides. So, without further ado, the best in slot gear for 20-29 protection paladins for PvP and PvE in Classic WoW.
Headpiece
Frostreaver CrownSunblaze Coif
Wicked Chain Helmet
Sentinel's Medallion
Gnomeregan Amulet
Tundra Necklace
Phalanx Spaulders
Green Iron Shoulders
Banded Pauldrons
Tigerstrike Mantle
Knight's Cloak
Archer's Cloak
Phantom Armor
Glimmering Mail Breastplate
Raptor Hunter Tunic
Jimmied Handcuffs
Renegade Bracers
Emissary Cuffs
Phalanx Gauntlets
Brawler Gloves
Wolfclaw Gloves
Highlander's Lamellar Girdle
Mail Combat Belt
Stonefist Girdle
Phalanx Leggings
Wicked Chain Legguards
Banded Leggings
Phalanx Boots
Pillager's Boots
Gnomeregan Band
Protector's Band
Basalt Ring
Talvash's Gold Ring
Jaina's Signet Ring
Tundra Ring
Dreamslayer
Protector's Sword
Vibroblade
Marbled Buckler
Commander's Crest
Bastion of Stormwind
Cobalt Crusher
Combatant Claymore
Deanship Claymore
Wicked Chain Helmet
Neck
River Pride ChokerSentinel's Medallion
Gnomeregan Amulet
Tundra Necklace
Shoulder
Thick Scale Shoulder PadsPhalanx Spaulders
Green Iron Shoulders
Banded Pauldrons
Back
Parachute CloakTigerstrike Mantle
Knight's Cloak
Archer's Cloak
Chest
Double Link TunicPhantom Armor
Glimmering Mail Breastplate
Raptor Hunter Tunic
Wrist
War Rider BracersJimmied Handcuffs
Renegade Bracers
Emissary Cuffs
Hands
Pillager's GlovesPhalanx Gauntlets
Brawler Gloves
Wolfclaw Gloves
Waist
Girdle of Golem StrengthHighlander's Lamellar Girdle
Mail Combat Belt
Stonefist Girdle
Legs
Dual Reinforced LeggingsPhalanx Leggings
Wicked Chain Legguards
Banded Leggings
Feet
Caverndeep TrudgersPhalanx Boots
Pillager's Boots
Ring Slot 1
Seal of WrynnGnomeregan Band
Protector's Band
Basalt Ring
Ring Slot 2
Plains RingTalvash's Gold Ring
Jaina's Signet Ring
Tundra Ring
Main Hand
Electrocutioner LegDreamslayer
Protector's Sword
Vibroblade
Shield
Resplendent GuardianMarbled Buckler
Commander's Crest
Bastion of Stormwind
Two-Handed
CorpsemakerCobalt Crusher
Combatant Claymore
Deanship Claymore
Dressing Room
If your focus is on Player versus Player action and if we choose from above the most useful in PvP (those that increase stamina, strength, armor, agility, and defense) then your toon should look like this: Protection Paladin BiS 20-29 PvP.
If you’re in a PvE mindset then with my chosen recommended best-in-slot items you would look like this: Protection Paladin BiS 20-29 PvE.
I built my Classic Protection set as a mishmash of both worlds centered around an aesthetic I find awesome: Protection Paladin 20-29 BiS Alternative Design.